Transmission lubrication and motor cooling system

ABSTRACT

The electric motor and transmission that apply power to the drive wheels of a vehicle are supplied with hydraulic fluid to lubricate the transmission and to cool the motor by a common fluidic circuit. The annular space between the motor shaft and a driveshaft provides a passage wherein fluid is distributed to the motor and the transmission under pressure. The rotor of the motor has axial passages through which the fluid flows from a radial passage connecting the annular space with the passages. At each axial end of the rotor fluid exiting the rotor, is thrown outward onto the inner surfaces of the stator windings. The fluid returns to a common sump by gravity from the motor and transmission.

CROSS-REFERENCE TO RELATED APPLICATION

This invention is related to the inventor's commonly assigned andcopending application Ser. No. 299,907 entitled "Concentric Powertrainfor Electric Vehicle."

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to a multiple speed ratio automatic transmissionfor use with an electrically driven automotive vehicle.

2. Description of the Prior Art

Conventional automatic transmissions used in vehicles powered byinternal combustion engines are not readily adapted for use in anelectrically driven vehicle.

The parasitic losses associated with operation of the hydraulic pump,control system and torque converter could reduce the operating range ofan electrical vehicle by approximately 15 percent. Furthermore, certainmajor automatic transmission components such as the hydrokinetic torqueconverter and reverse gearing are unnecessary in an electric vehiclethat uses an a.c. induction motor. Also the final drive or axial ratioused with conventional automatic transmissions would limit the operatingspeed of the electrical motor and this would result in substantial cost,weight and size penalties.

The most favorable balance among costs, weight, efficiency and packagesize for an electric vehicle powertrain is realized with electric motorsthat operate in the range between 8000 and 10,000 rpm with an automatictransmission compatible with these speeds. An automatic transmissiondevelops the maximum vehicle driving range through efficient control ofthe motor operation and because regenerative braking, which recoversbraking energy to drive the vehicle.

A variety of motor-transmission configurations are possible in the frontwheel drive vehicles. Two or three rotational axes interconnected bygear or chain transfer drives are generally employed to provide steptransmission ratios and the final drive ratio. The differential bevelgear system is usually located on the drivewheel axis. A front wheeldrive system wherein the motor and transmission are mounted transverselywith respect to the fore and aft axis of the vehicle, must be a highlycompact unit and preferably one in which the high speed a.c. motor,automatic transmission and final drive have a common axis with the wheelaxis.

SUMMARY OF THE INVENTION

A high speed a.c. motor, automatic transmission and final drive areintegrated in a single transaxle system according to this invention.Planetary gearing produces multiple speed ratios and the final driveratio. The motor rotor shaft is hollow allowing one drive shaft to passthrough its center from the differental bevel gear assembly to auniversal constant velocity joint. The annular space between the rotorshaft inside surface and the outer surface of the driveshaft is employedas part of the hydraulic circuit that supplies fluid to the motor forcooling and to the transmission for lubrication.

The conventional automatic transmission practice of driving thehydraulic oil pump directly by the prime mover, in this case an electricmotor, would result in an unnecessary power loss under most operatingconditions and would limit the vehicle driving range. Here, instead, thehydraulic supply pump is driven by a separate small motor which operatesonly on demand. Full pump displacement is required only during atransmission upshift interval of approximately 0.5 seconds. Otherwise,the hydraulic supply pump need be operated only occasionally toaccommodate system leakage. A second electrically driven oil pumpoperating at low pressure, at approximately 15 psi, circulates oil to anoil cooler and provides motor and transaxle lubrication and motorcooling capability. Both pumps draw oil from a common transaxle oil sumpthat supplies hydraulic fluid for both the lubrication and coolingsystems.

In a dual flow motor cooling system, the motor rotor is cooled directlythrough passages formed in the rotor laminations. The rotor stator iscooled by oil flowing from the rotor radially outward on the ends of thestator windings through the action of centrifugal force. The heated oilreturns by gravity to the sump from which the oil is carried to the oilcooling system. The oil cooler includes a small radiator with anelectrically driven cooling fan that is activated upon demand to controlthe oil temperature. This avoids an unnecessary power loss when oiltemperature is lower than the upper limit. Heat from the oil isdelivered to the atmosphere or used to heat the passenger compartment.Cooling oil flowing over the stator surface is superior to external oiljacket cooling of the stator and to conventional air cooling through therotor-stator air gap.

Hydraulic fluid returning to the motor-transmission assembly from theoil cooling system circulates with the transmission to lubricatesurfaces requiring lubrication and within the electric motor principallyto carry away excess heat. The fluid returns by gravity to a common sumpat the bottom of the assembly where it is delivered to a pump thatpressurizes the oil cooling system and the circuitry within thetransmission and motor.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1A is an elevation cross section through the centerline of anautomatic power transmission according to this invention.

FIG. 1B is an elevation cross section through the centerline of aninduction motor that drives the transmission of FIG. 1A.

FIG. 2 shows schematically the gear arrangement and clutches of thetransmission of FIG. 1A.

FIG. 3 shows schematically the gear arrangement and clutches of analterate transmission having three planetary gear units for use with ana.c. induction motor.

FIG. 4 is a schematic diagram of a system by which heat can be removedfrom the oil used to lubricate the transmission and to cool the rotorand stator of the motor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An a.c. induction motor 10 is mounted coaxially with a two-speedplanetary automatic transmission 12 and constant velocity joints 14, 16which transmit power to the right and left drive wheels of the vehicle.The rotor shaft 18 of the motor is a sleeve shaft supported at one endon a bearing 20 whose outer race is supported on the motor casing 22.The opposite end of the motor shaft is journalled at 24 on a supportsurface of the transmission casing 26, which is joined to the motorcasing by the attachment bolts 28.

The differential mechanism 30 transmits torque to a first drive shaft 32that extends coaxially with the transmission and motor and is locatedwithin and supported on the inner surface of the rotor shaft 18. Asecond drive shaft 34 transmits torque to the inner constant velocityjoint 16 of a half shaft assembly that transmits power to the left drivewheel of the vehicle. Oil seals 36, 37 seal the lubrication systemadjacent bearing 20 and the support surface for the second driveshaft34.

The two-speed planetary automatic transmission for use with the motor 10has a first stage that includes a sun gear 40 that may be formedintegrally with the rotor shaft 18. Multiple planetary pinions 42located in the annular space within the ring gear 44 are in continuousmeshing engagement with sun gear 40 and ring gear 44. Each pinion 42 ismounted for rotation by needle bearings 46 on a shaft 48 that issupported at each end by a planetary pinion carrier 50. Carrier 50 issplined at 52 to an axially extending portion of a second sun gear 54that is a part of second transmission stage. The mounting flange for pin43 at the opposite axially end of carrier 50 is rotatably supported onthe annular portion 56 of the transmission casing upon which the rotorshaft is journalled at 24.

Ring gear 44 is connected to the inner driver element 57 of anoverrunning clutch 58 whose outer driven element 50 is secured to thetransmission casing against rotation. Ring gear 44 is also connected toa disc clutch 60 that operates to produce reverse drive, hill braking inlow gear and regenerative braking. When clutch 60 is applied, ring gear44 is fixed to the transmission casing against rotation. Anotherhydraulically actuated clutch, the high gear clutch 62, operates toconnect ring gear 44 to the carrier 64 of the second transmission stage.Clutch 62 includes a piston 66 that moves within a cylinder 67. Returnsprings 68 located within the annulus of the clutch operate to returnpiston 66 to the position shown in FIG. 1 when hydraulic pressure isremoved from cylinder 67. When piston 66 is actuated by hydraulic fluid,the discs of the clutch are forced into frictional engagement with discsthat are connected to carrier 64 upon which the planetary pinions of thesecond stage are mounted by pin 70. High gear clutch 62 produces adriving connection between ring gear 44 and the carrier 64.

The second transmission stage includes the second sun gear 54 which isin continuous meshing engagement with multiple second stage planetarypinions 72 that are located within the annular region defined by thesecond ring gear 74. Pinions 72 are mounted for rotation on shaft 70which is supported on the second stage carrier 64. Ring gear 74 ispermanently fixed against rotation to a second portion of thetransmission housing 76 that is mechanically joined to the firsttransmission housing 26.

The differential mechanism 30 includes a bevel pinion shaft 78 that isjoined by multiple roll pins 80 to the carrier 64 of the secondtransmission stage. Upper and lower bevel pinions 82, 84, fixed securelyto pinion shaft 78, are held in continuous meshing engagement with bevelgears 86, 88, respectively, that are splined to the driveshafts 32, 34.A parking gear 90 integrally formed with carrier 64 operates to preventrotation of driveshafts 32, 34 because it is fixed by the pin 80 tobevel pinion shaft 78.

To disposition the transmission for first gear forward speed operationneither of the friction disc clutches need be engaged. Instead,overrunning clutch 58 is arranged so that its inner race or drivingmember 57 transmits torque to the outer race 59, thus fixing ring gear44 against rotation by way of the fixed connection between the outerrace and the transmission casing. Pinion carrier 50, the driven memberof the first stage, transmits power to the second sun gear 54 throughthe spline connection 52. The second planetary stage has its ring gear74 permanently fixed against rotation, therefore, the planetary pinioncarrier 60 is the driven element of the second stage. The bevel pinionshaft 78 rotates about the central axis of the transmission as carrier64 rotates. Power is therefore transmitted to the driveshafts 32, 34 byway of the engagement of the bevel pinions 82, 84 with the bevel gears86, 88.

High speed ratio results when high gear clutch 62 is engaged and clutch60 is disengaged. When this occurs, overrunning clutch 58 does notoperate to lock ring gear 44 to the transmission casing, but ratherconnects ring gear 44 to pinion carrier 64. Pinion carrier 50 of thefirst stage is permanently connected to sun gear 54 on the second stagethrough spline 52. The torque delivery path for high speed ratiooperation includes the first sun gear 40, which is driven by the rotorshaft 18; the first planet pinion carrier 50, which drives the secondsun pinion 54; and the first ring gear 44, which is drivably connectedby clutch 62 to the second planet pinion carrier 64. The second ringgear 74 fixed to the transmission casing provides the torque reactionfor the transmission in high gear. Pinion carrier 64 drives the bevelpinion shaft 78 in rotation about the central axis of the transmissionand bevel pinions 82, 84 drive bevel gear 86, 88 thereby transmittingpower to the driveshafts 32, 34.

Reverse drive results when the rotational direction of the motor isreversed and reverse clutch 60 is applied. When the direction of themotor is reversed, clutch 58 overruns but first ring gear 44 is fixedagainst rotation when the reverse clutch 60 is applied. In thisinstance, the torque delivery path is identical to that of the low speedratio forward drive previously described. Rotor shaft 18 drives the sungear 40 and first planet carrier 50 drives second sun gear 54. The firstand second ring gears are fixed against rotation and provide torquereaction points for the transmission. Output power is transmitted by thesecond planetary carrier 64 to the bevel pinion shaft 78 which transmitstorque to the driveshafts 32, 34.

A second embodiment of the transmission, one that employs a thirdplanetary gear unit to produce the two forward speed ratios and thereverse drive, is shown in FIG. 3.

In FIG. 3, components of the first and second planetary gear units havethe same identifying numbers as the components shown in FIG. 2 to whichthey correspond. Rotor shaft 18 transmits drive from the electric motor10 to the first sun gear 40. The first ring gear is connected to thedriving elements of the overrunning clutch 58 whose driven element isfixed to the transmission casing against rotation. The first planetpinion set is rotatably mounted on the carrier 50, which drives thesecond sun gear 54. A second set of planet pinions is rotatably mountedon a carrier 64 which drives a third sun gear 92. The ring gear 74 ofthe second planetary unit can be selectively fixed against rotation byway of reverse clutch 94. Similarly, the second ring gear may beselectively connected by application of high speed ratio clutch 96 to athird planet pinion carrier 98 on which a third set of planetary pinions100 are rotatably mounted. The third ring gear 102 is permanently fixedto the transmission casing against rotation.

First speed ratio results although neither clutch 94 or 96 is applied.Instead, overrunning clutch 58 fixes the first ring gear againstrotation and provides a second torque reaction point in addition to thatof third ring gear 102. Carrier 50, which drives the second sun gear 54,is the driven element of the first planetary set. Carrier 64, whichdrives the third sun gear 92 is the driven element of the secondplanetary gear set. Finally, the third pinion carrier 98 drives thebevel pinion shaft 78, which distributes power to the driveshafts 32,34.

High speed ratio operation results when the high speed ratio clutch 96is applied and the reverse clutch 94 is inoperative. In this case, ringgear 102 provides the only torque reaction point for the transmission,since clutch 58 is overrunning. Carrier 50, the driven element of thefirst gear set, drives the second sun gear 54. Carrier 64, the drivenelement of the second gear set, drives sun gear 92. The first and secondring gears 44, 74 are drivably connected through clutch 96 to the thirdpinion carrier 98, which drives the bevel pinion shaft 78.

Reverse drive is accomplished with the transmission arrangement of FIG.3 upon application of the reverse clutch 94 provided high speed gearratio clutch 96 is not applied. Clutch 94 prevents rotation of the firstand second ring gears 44, 74 as did the overrunning clutch 58 in the lowspeed forward drive condition. For reverse drive, however, the directionof rotation of the motor and rotor shaft 18 is reversed from that of lowspeed forward drive. Pinion carriers 50 and 64 drive the sun gears 54,92 of the second and third gear units. Since each ring gear is fixedagainst rotation, the driven member is planet carrier 98 which transmitspower to the bevel pinion shaft 78.

The braking for an electric vehicle can be used to recharge thebatteries provided the control system for the vehicle is adapted to runthe motor as a generator when braking occurs, rectify the a.c. currentto a d.c. current and charge the battery during the braking action. Thisregenerative braking system can be used in cooperation with the powertrain of this invention if the control system is adapted to actuate thereverse clutch 60 or 94 when braking occurs. The electrical brake torqueused to drive the generator during regenerative braking is recoveredfrom the wheels of the vehicle and transmitted back through thetransmission provided the transmission is disposed as has been describedfor reverse drive.

Similarly, a hill braking function, whereby kinetic energy of thevehicle can be recovered and converted to electrical energy to rechargethe batteries when the vehicle is rolling down hill, can be accommodatedby a control system that is adapted to sense the need for braking inthis condition. When hill braking is integrated in the control scheme,the transmission will be disposed for reverse drive so that power istransmitted from the driveshafts through the differential and thetransmission to drive rotor shaft 18. This is accomplished when thereverse drive and regenerative braking clutch 60 or 94 is actuated andthe high speed ratio clutch 62 or 96 is disengaged.

Preferably, the motor that drives the electric vehicle through thetransmission of this invention, is an hermetically sealed a.c. inductionmotor. The motor stator and rotor are cooled by the circulation of oilwhich is used also to lubricate the transmission. The motor, coolingsystem and transaxle lubrication system share a common oil pump andsump.

Referring now to FIGS. 1A, 1B and in particular to FIG. 4, the electricmotor 10 and transmission 12 are shown assembled about a common axisrepresenting the axis of the driveshafts that transmit power to thedrive wheels of the vehicle. If the motor-transmission assembly is usedin a front wheel drive vehicle, power is transmitted to the wheelsthrough constant velocity joints 14 and 16. If, however, the transaxleis used to drive the rear wheels of the vehicle, the differentialtransmits power from the driveshafts to the wheels without the need forthe constant velocity joints. The cooling and lubricating oil flows bygravity into a sump 104. The sump is connected by oil line 106 to a lowpressure circulating pump 108 driven by a variable speed electric motor.A control valve 110 directs the flow of oil to a radiator 112 or to aheater core 114. The heat content of the oil is transferred by theradiator to an air stream forced through the air radiator by anelectrically driven fan which delivers the heat to the atmosphere. Thecooled oil is carried in oil line 116 and through an oil inlet duct 118through which the oil enters the transaxle assembly. If control valve110 directs oil to the heater core, the heat content of the oil can beexchanged with air passing through the heater core to heat the passengercompartment. The cooled oil is carried by line 120 and inlet oil line118 to the transaxle.

Within the transmission, the oil is directed to the needle bearings 46that support the first planetary pinion set on pin 48 through oil lines122 formed in the transmission casing and in the carrier 50. OIl isdelivered to the annular space 124 between the inside diameter of therotor shaft 18 and the outside diameter of the driveshaft 32 and issupplied by way of this passage through bushings 126 and thrust washers128 to lubricate the gears of the second planetary gear unit. Oil isdelivered under approximately 15 psi. pressure to the inlet duct 118.Oil flows by gravity from the lubricated gear surfaces to the sump 104.

The annular space 124 is used to supply coolant to the rotor and statorof the motor. Radially directed ducts 130 intersecting passage 124 carrycoolant to the rotor 132 through which it flows in both axial directionsin ducts 142. The rotor 132 is an assembly of laminants arranged inface-to-face abutment to form a rotor stack. Each laminant has multipleholes through its thickness through which the cooling oil flows. Uponexiting the rotor, oil is thrown by centrifugal force against the innerdiameter of the stator windings 136 at each axial end of the rotor. Theoil wets the perimeter of the windings and flows by gravity throughdrain holes 138, 140 into the sump.

Other radial holes 144, 146 formed in rotor shaft 18 intersect theannular space 124 immediately within the inner radius of the windings136 and provide a passage through which oil is directed against thesurface of the windings.

Having described a preferred embodiment of my invention, what I claimand desire to secure by U.S. Letters Patent is:
 1. In an electric motorand mechanical transmission assembly, a system for supplying fluid thatlubricates the transmission and cools the motor comprising:a hollowrotor shaft connecting the rotor of the electric motor to thetransmission input having radially directed holes located along itslength; a differential mechanism driven by the transmission adapted totransmit power to first and second driveshafts that extend outward fromthe differential mechanism, at least one of said drivenshafts and therotor shaft defining an annular passage therebetween through which thefluid passes from the fluid source to the transmission and to the motor;a multiple speed ratio power transmission connected to the driveshafthaving fluid ducts connecting the annular passage to meshing gearsurfaces and bearing support surfaces; a source of pressurized fluid; anelectric motor having a rotor formed with an axially directed fluid ductand a radial duct for connecting the annular passage to the axial fluidduct, a stator winding located radially outward from and at axiallyopposite ends of the axial fluid duct and radially outward from theradially directed holes of the rotor shaft, whereby the fluid is thrownby centrifugal force from the annular passage through the radial holesof the rotor shaft and onto the surfaces of the stator winding and thefluid is forced by centrifugal force from the annular passage throughthe radially and axially directed fluid ducts of the rotor and onto thesurfaces of the stator winding; and passage means for directing fluid toa sump from which the source is supplied with fluid.
 2. The system ofclaim 1 wherein the transmission further includes a first planetarygearset having a sun gear formed on the rotor shaft, a ring gear, a setof planetary pinions in meshing engagement with the sun gear and thering gear, a pinion carrier, a pinion shaft mounted on the carrier,bearing means mounted on the pinion shaft for rotatably supporting thepinions on the carrier and fluid ducts formed in the carrier and pinionshaft for hydraulically connecting the fluid pressure source to thebearing means.
 3. The assembly of claim 2 further comprising:a hyraulicpump communicating with the sump means for producing said source ofpressurized fluid; a heat exchanger hydraulically connected to the pumpfor transferring heat from the fluid to the atmosphere or to thepassenger compartment of the vehicle, and means hydraulically connectingthe heat exchangers to the transmission and motor.
 4. The system ofclaim 1 wherein the transmission further includes a planetary gearsethaving a sun gear rotatably supported on the differential mechanism, aring gear, a set of planetary pinions in meshing engagement with the sungear and ring gear, a pinion carrier, a pinion shaft mounted on thecarrier, means mounted on the pinion shaft for rotatably supporting thepinions on the carrier, the sun gear and differential mechanism defininga fluid passage therebetween for hydraulically connecting the annularpassage to the surfaces of the pinion teeth and to the bearing means. 5.The system of claim 4 wherein the sun gear and pinion carrier define afluid passage therebetween for hydraulically connecting the annularpassage to the surfaces of the pinion teeth and to the bearing means. 6.The system of claim 1 wherein the transmission further includes:a firstplanetary gearset having a sun gear formed on the rotor shaft, a ringgear, a set of planetary pinions in meshing engagement with the sun gearand the ring gear, a pinion carrier, a pinion shaft mounted on thecarrier, bearing means mounted on the pinion shaft for rotatablysupporting the pinions on the carrier and fluid ducts formed in thecarrier and pinion shaft for hydraulically connecting the fluid pressuresource to the bearing means; a second planetary gearset having a sungear rotatably supported on the differential mechanism, a second ringgear, a second set of planetary pinions in meshing engagement with thesecond sun gear and second ring gear, a second pinion carrier, a secondpinion shaft mounted on the carrier, second bearing means mounted on thesecond pinion shaft for rotatably supporting the pinions on the carrier,the second sun gear and differential mechanism defining a fluid passagetherebetween for hydraulically connecting the annular passage to thesurfaces of the pinion teeth and to the second bearing means.
 7. Thesystem of claim 6 wherein the second sun gear and second pinion carrierdefine a fluid passage therebetween for hydraulically connecting theannular passage to the surfaces of the pinion teeth and to the secondbearing means.